diff --git a/refs.c b/refs.c
index 65eea3eb77..ee87081746 100644
--- a/refs.c
+++ b/refs.c
@@ -2325,7 +2325,7 @@ int refs_verify_refname_available(struct ref_store *refs,
 				  const char *refname,
 				  const struct string_list *extras,
 				  const struct string_list *skip,
-				  int initial_transaction,
+				  unsigned int initial_transaction,
 				  struct strbuf *err)
 {
 	const char *slash;
diff --git a/refs.h b/refs.h
index 980bd20cf2..95baf194ba 100644
--- a/refs.h
+++ b/refs.h
@@ -110,7 +110,7 @@ int refs_verify_refname_available(struct ref_store *refs,
 				  const char *refname,
 				  const struct string_list *extras,
 				  const struct string_list *skip,
-				  int initial_transaction,
+				  unsigned int initial_transaction,
 				  struct strbuf *err);
 
 int refs_ref_exists(struct ref_store *refs, const char *refname);